Scanning of large objects, e.g. large maps or technical drawings, is conventionally performed by using a plurality of image sensors as it is a difficult and expensive task to manufacture large single image sensors. Examples of image sensors are charge coupled device (CCD) or contact image sensors (CIS). Differences between image sensors, however, create visible artefacts in the scanned images. The intensity of a scanned medium may look different dependent on which image sensor is used. This makes the scanned images less perceptually appealing. As the differences are non-static, compensation is a challenging task.
EP 2 091 223 entitled “Image reading device and image forming apparatus” discloses an optical scanner with multiple cameras that each outputs line signals. The cameras are arranged to each view a portion of a line on a document to be scanned. The cameras view the line with a certain overlap such that intensity information is recorded by two cameras in the overlapping regions of the line. A complete line on the document is reproduced by combining line signals from the cameras. The line signals are processed in the overlapping area to compensate for an intensity boundary, e.g. a visible artefact at the stitching point between cameras, which may occur. The method, however, still creates visible artefacts in the generated images.
Thus, it remains a problem to improve the image quality of large-format scanners to compensate for differences between individual image sensors.